The present invention relates to an air damper to prevent extraneous vibration and shock from transmission to a precision electronic and mechanical component incorporated in a body of equipment.
In recent years, a precision electronic and mechanical component including a magnetic disc device, a DVD (digital versatile disc) or CD (compact disc) drive is intended to reduce in size and weight and to configure as one unit so as to be suitable for portable use. In the precision electronic and mechanical component, in order to improve a vibration-proof characteristic or a shock-proof characteristic, the component is commonly suspended in a body of equipment by using a shock absorbing member such as an air damper.
An air damper in the prior art is disclosed in the Japanese published unexamined patent application Hei 5-159552, for example. The air damper in the prior art comprises an outer casing of which two tire-shaped members are stacked in a manner of one above the other in the axial direction. The outer casing includes a compression coil spring therein. A driving section housing provided with the precision electronic and mechanical component to be supported is inserted in a constricted part formed between two tire-shaped members, thereby holding. The upper face and the lower face of the outer casing are in contact with a subframe and a support frame which are fixed to the body of equipment, respectively, and the outer casing is mounted between the subframe and the support frame with a shank having threads. The outer casing has a projection on the inner wall to configure an auxiliary damping structure in operative connection with the shank.
In the prior art, when extraneous vibration is transmitted to the air damper from the body of equipment through the subframe and the support frame, the outer casing and the compression coil spring deform, thereby absorbing the vibration. Additionally, the outer casing is made airtight by the subframe, the support frame and the shank, and the vibration is also absorbed by a cushiony action of air in the airtight outer casing. Moreover, the above-mentioned projection deforms in dependence on the moving of the shank, and absorbs the vibration.
In the above-mentioned air damper of the prior art, the compression coil spring is included in the outer casing.
When the frequency of the extraneous vibration is equal to the natural frequency of the compression coil spring, the extraneous vibration is amplituded by resonance and transmitted to the precision electronic and mechanical component to be supported. Once vibration occurs on the compression coil spring, the vibration continues for a while. It is difficult to absorb the vibration within a short period of time. When the amplitude of the extraneous vibration or shock exceeds a predetermined value, the compression coil spring is compressed to the compression limit, and can not absorb any more vibration.
It is difficult to reduce in size and in weight and to simplify the structure of the outer casing because of the existence of the compression coil spring therein. Since the subframe must be provided in the body of equipment in order to make airtight the outer casing, the structure of the body of equipment can not be simplified.
The outer casing of the air damper of the prior art is not directly fixed to the shank. Therefore, a positional displacement is liable to occur between the outer casing and the shank due to an external force such as vibration or shock, and thereby the shank is liable to tilts relative to the outer casing. Consequently, the outer casing, the compression coil spring and the projection are pressed by the tilted shank and result in deformed states. In the above-mentioned states, the air damper can not absorb the vibration and shock.
An object of the present invention is to provide an air damper which can damp and absorb vibration and shock having large amplitudes, and is reduced in size and in weight.
An air damper of the present invention to be mounted between a support board having an object to be supported and a frame fixed to a body of equipment comprises a casing including at least two hollow members which are made of an elastic material and stacked vertically, and a fastening member. The support board is held between two hollow members of the casing, and the hollow member of a lowest step is in close contact with the frame.
The fastening member is inserted into the casing in the axial direction of both the stacked hollow members, and fixes the casing to the frame so as to make airtight.
According to this configuration, vibration and shock having large amplitudes can be damped and absorbed by utilizing the deformation of the casing and an air spring action of the air enclosed in the casing. Since the air spring is utilized, the air damper is easily reduced in size and weight.
An air damper of another aspect of the present invention comprises a casing of an elastic material, including at least two hollow members connected with an intermediate section having a communication opening, and supporting a support board having an object to be supported. at the intermediate section. One of the hollow members includes a thin walled portion of a predetermined diameter at an end portion thereof, and an upper opening having a diameter smaller than the diameter of the thin walled portion, formed at a central portion of the thin walled portion. The other hollow member includes a lower opening having a diameter smaller than the predetermined diameter at an end. Furthermore, the air damper comprises a fastening member including a shank of the approximately same diameter as the outer diameter of the thin walled portion, a shoulder of a diameter larger than the diameter of the lower opening and threads attached to the shoulder, having a diameter smaller than the diameter of the lower opening.
When the fastening member is attached to the frame so that the shank of the fastening member passes through the upper opening, the communication opening and the lower opening of the casing, the shoulder fixes the periphery of the lower opening to the frame in an airtight manner. Since the diameter of the upper opening is made smaller than the diameter of the shank and the thin walled portion is disposed in the periphery of the upper opening, the thin walled portion is folded inward, and airtightness is maintained between the upper opening and the shank. Since the diameter of the lower opening is made smaller than the diameter of the shoulder of the fastening member, the shoulder presses the periphery portion of the lower opening, and airtightness is maintained between the lower opening and the fastening member.
An air damper of a further aspect of the present invention comprises an air passage to communicate the interior of the casing with the outside in addition to the elements in the above-mentioned configuration.
According to this configuration, in addition to the above-mentioned deformation of the casing and the air spring action, an air-resistance action of the air passing through the air passage improves the absorbing characteristic of the vibration and shock, and the vibration and shock are absorbed within a short period of time.